High purity fine metal powders and methods to produce such powders

ABSTRACT

A method of producing metal and alloy fine powders having purity in excess of 99.9%, preferably 99.999%, more preferably 99.99999%. Fine powders produced are of size preferably less than 10 micron, more preferably less than 1 micron, and most preferably less than 100 nanometers. Methods for producing such powders in high volume, low-cost, and reproducible quality are also outlined. The fine powders are useful in various applications such as biomedical, sensor, electronic, electrical, photonic, thermal, piezo, magnetic, catalytic and electrochemical products.

1. RELATED APPLICATIONS

[0001] This application is a divisional application of co-pending U.S.Ser. No. 09/638,977 filed Aug. 15, 2000, which claims priority to U.S.provisional patent application serial No. 60/182,692 entitled “Very HighPurity Fine Powders and Methods to Produce Such Powders” filed Feb. 15,2000, the specifications of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 2. Field of the Invention

[0003] The present invention relates, in general, to high puritypowders, and, more particularly, to high purity fine powders and methodsto produce high purity fine powders.

[0004] 3. Relevant Background

[0005] Powders are used in numerous applications. They are the buildingblocks of electronic, telecommunication, electrical, magnetic,structural, optical, biomedical, chemical, thermal, and consumer goods.On-going market demand for smaller, faster, superior and more portableproducts has resulted in miniaturization of numerous devices. This, inturn, has demanded miniaturization of the building blocks, i.e. thepowders. Sub-micron and nanoscale (or nanosize, ultrafine) powders, witha size 10 to 100 times smaller than conventional micron size powders,enable quality improvement and differentiation of productcharacteristics at scales currently unachievable by commerciallyavailable micron-sized powders.

[0006] Nanopowders in particular and sub-micron powders in general are anovel family of materials whose distinguishing feature is that theirdomain size is so small that size confinement effects become asignificant determinant of the materials' performance. Such confinementeffects can, therefore, lead to a wide range of commercially importantproperties. Nanopowders, therefore, represent an extraordinaryopportunity for design, development and commercialization of a widerange of devices and products for various applications. Furthermore,since they represent a whole new family of material precursors whereconventional coarse-grain physiochemical mechanisms are not applicable,these materials offer unique combinations of properties that can enablenovel and multifunctional components of unmatched performance. Bickmoreet al. in U.S. Pat. No. 5,984,997, which along with the referencescontained therein are hereby incorporated by reference in full, teachsome applications of sub-micron and nanoscale powders.

[0007] Higher purity materials are needed in electronic applications.For example, silicon is now routinely purified to levels greater than99.99999% for electronic applications. It is expected that the purityrequirements for electronic applications will increase even further. Notonly silicon, but other elements from the periodic table and othercompounds (metal, semimetal, inorganic or organic) are and will bedesired in greater and greater purity. Crystals, bulk materials, fibers,coatings and films are all desired in high purity. Impurities causefailures or defects in electronic and other applications. Higher puritychemicals and materials offer a means of greater product reliability andperformance. They also offer means to extend the life of products. Forexample, batteries prepared from high purity materials offer longer lifeand superior performance. Existing applications that use commerciallyavailable low purity chemicals and materials may all benefit from higherpurity chemicals and materials. Since many chemicals and materials areused in the form of powders at some stage, high purity powders areneeded and are expected to be needed in the future.

[0008] Commonly used high purity powder production techniques are basedon starting with commercial grade impure powders and then applyingpurification techniques to reduce impurities. Some illustrations includeleaching, extraction and precipitation, melting, sublimation of volatileimpurities, decomposition, chemical reaction, dissolution andcrystallization, and electrochemical techniques. These methods areexpensive, slow, low volume, and difficult when purities greater than99.99% are desired. This is one reason why powders with purity greaterthan 99.9% often enjoy price premiums that are 100 fold higher thanreadily available low purity powders (95 to 98%).

[0009] Padhi and Pillai (U.S. Pat. No. 5,955,052) teach a process whichprovides high purity lithiated manganese oxide powders, and is herebyincorporated by reference. Their process is a chemical ion exchangereduction method. They do not teach how to reach product puritiesgreater than 99.9%, and their process is expected to be expensive.

[0010] Schloh (U.S. Pat. No. 5,711,783) teaches a process for preparinghigh purity metal powder by reacting one or more volatile alkoxidecompounds with a reducing gas, and is hereby incorporated by reference.The process yields a product with very low metal impurities (in theparts-per-million (ppm) range), but with carbon and oxygen impurities.The process is not suitable for production of oxides, carbides, and manyother compounds.

[0011] Kambara (U.S. Pat. No. 5,722,034, which is hereby incorporated byreference) teaches a method of manufacturing a high-purity refractorymetal or alloy using a novel electron beam refining method. This methodstarts with powders or lumps, but ends up with a sintered material. Themethod is reported to yield 99.999% pure metal and alloys. This methodis anticipated to lead to higher costs. The teachings do not suggestmethods for producing high purity inorganics (e.g., oxides).Furthermore, the teachings do not suggest ways to produce high puritypowders.

[0012] Axelbaum and DuFaux (U.S. Patent No. 5,498,446, which is herebyincorporated by reference) teach a method and apparatus for reactingsodium vapor with gaseous chlorides in a flame to produce nanoscaleparticles of un-oxidized metals, composites and ceramics. The inventionrelates to a development in the production of sub-micron particles and,more particularly, to a development in the flame synthesis ofun-agglomerated, nanometer-sized particles of characteristically highpurity. The un-oxidized high purity is achieved because of the coatingwith sodium chloride formed during the flame process. The sodium vaporprocess is difficult to operate, increases safety concerns, is expensiveand is difficult to scale up. It is expected that the powders producedhave sodium and chloride contamination arising from the synthesismechanism used. The teachings are limited to producing particles thatare compatible with sodium flame chemistry. Furthermore, the teachingsdo not specify methods to produce complex materials such as multimetaloxides, carbides, nitrides, borides, and the like.

[0013] Krstic (U.S. Pat. No. 5,338,523, and which is hereby incorporatedby reference) teaches a process for the production of high purity, highsurface area, sub-micron size transition metal carbides and borides. TheKrstic method comprises mixing transition metal oxide with carbon in anamount sufficient to form the corresponding carbide or boride. Thereactants are heated at a temperature of higher than 1000° C. under asmall pressure of non-reacting gas and then holding the temperaturewhilst applying simultaneously sub-atmospheric pressure and agitationuntil the reaction is complete. Krstic teachings suggest how lowercarbon impurities can be achieved over the state of the art, but do notsuggest how purities in excess of 99.9% can be achieved. The process isalso limited in its economic attractiveness.

DEFINITIONS

[0014] Fine powders, as the term used herein, are powders thatsimultaneously satisfy the following:

[0015] 1. particles with mean size less than 100 microns, preferablyless than 10 microns, and

[0016] 2. particles with aspect ratio between 10⁰ and 10⁶.

[0017] Submicron powders, as the term used herein, are fine powders thatsimultaneously satisfy the following:

[0018] 1. particles with mean size less than 1 micron, and

[0019] 2. particles with aspect ratio between 10⁰ and 10⁶.

[0020] Nanopowders (or nanosize or nanoscale powders), as the term usedherein, are fine powders that simultaneously satisfy the following:

[0021] 1. particles with mean size less than 250 nanometers, preferablyless than 100 nanometers, and

[0022] 2. particles with aspect ratio between 100 and 10⁶.

[0023] Pure powders, as the term used herein, are powders that havecomposition purity of at least 99.9%, preferably 99.99% by metal basis.

[0024] Powder, as the term used herein encompasses oxides, carbides,nitrides, chalcogenides, metals, alloys, and combinations thereof. Theterm includes particles that are hollow, dense, porous, semi-porous,coated, uncoated, layered, laminated, simple, complex, dendritic,inorganic, organic, elemental, non-elemental, composite, doped, undoped,spherical, non-spherical, surface functionalized, surfacenon-functionalized, stoichiometric, and non-stoichiometric form orsubstance.

SUMMARY OF THE INVENTION

[0025] Briefly stated, the present invention involves a method ofproducing metal and alloy fine powders having purity in excess of 99.9%,preferably 99.999%, more preferably 99.99999%. Fine powders produced areof size preferably less than 10 micron, more preferably less than 1micron, and most preferably less than 100 nanometers. Methods forproducing such powders in high volume, low-cost, and reproduciblequality are also outlined. The fine powders are useful in variousapplications such as biomedical, sensor, electronic, electrical,photonic, thermal, piezo, magnetic, catalytic and electrochemicalproducts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 shows an exemplary overall approach for production highpurity powders in accordance with the present invention;

[0027]FIG. 2 shows a schematic flow diagram of a thermal process for thecontinuous synthesis of nanoscale powders in accordance with the presentinvention; and

[0028]FIG. 3 shows a schematic flow diagram of an alternative thermalprocess for the continuous synthesis of nanoscale powders.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] This invention is directed to very high purity fine powders ofoxides, carbides, nitrides, borides, chalcogenides, metals, and alloys.The scope of the teachings includes purities that exceed 99.9%, 99.99%,preferably 99.999%, more preferably 99.99999%, and most preferably99.9999999%. Fine powders discussed are of size less than 100 microns,preferably less than 10 micron, more preferably less than 1 micron, andmost preferably less than 100 nanometers. Methods for producing suchpowders in high volume, low-cost, and reproducible quality are alsooutlined.

[0030]FIG. 1 shows an exemplary overall approach for production highpurity powders in accordance with the present invention. This method canbe used to produce powders that are coarse and pure, but is particularlyuseful for sub-micron and nanoscale powders. The process shown in FIG. 1begins at 101 with a metal containing precursor (for example but notlimited to, emulsion, fluid, particle containing liquid slurry, or watersoluble salt).

[0031] A key feature of this invention is preparing high purity fluidprecursors for powders of desired composition in step 102. Numerousmethods are available to purify fluids. To illustrate but not limit,distillation, membranes, electrochemical cells, ion exchange, andchromatography are a few unit operations that can achieve high purity.Techniques are now commercially available that can achieve parts perbillion purity levels. These techniques and new discoveries are enablingthe production of fluids that have parts per trillion purities.

[0032] In a preferred embodiment for the present invention,environmentally benign, safe, readily available, high metal loading,lower cost fluid precursors are preferred. The precursor may be a gas,single phase liquid, multiphase liquid, a melt, fluid mixtures andcombinations thereof. Illustration of precursors includes but does notlimit to metal acetates, metal carboxylates, metal ethanoates, metalalkoxides, metal octoates, metal chelates, metallo-organic compounds,metal halides, metal azides, metal nitrates, metal sulfates, metalhydroxides, metal salts soluble in organics or water, and metalcontaining emulsions. Multiple metal precursors may be mixed if complexpowders are desired. To illustrate but not limit, barium precursor andtitanium precursor may be mixed to prepare high purity barium titanatepowders; alternatively, yttrium precursor, barium precursor, and copperprecursor may be mixed in correct proportion to yield high purity YBCOpowder for superconducting applications. In all cases, it is necessaryto use precursors that are more than 99.9% pure to begin with if theultimate powder purity desired is 99.9%. If purities greater than x % isdesired, one or more precursors that are mixed and used must all beequal to or greater than x % pure to practice the teachings herein.

[0033] When the objective is to prepare an oxide, a preferred embodimentof this invention is to use a precursor in which the oxygen-to-carbonelemental ratio in the precursor molecule is high. Alternatively or incombination, a reactive fluid may be added with the precursor to thereaction zone which provides excess oxygen. Some illustrative examplesinclude but are not limited to oxygen gas and air.

[0034] When the objective is to prepare a carbide, a preferredembodiment of this invention is to use a precursor with anoxygen-to-carbon elemental ratio in the precursor molecule less than 0.1and more preferably less than 1.0, and most preferably less than 2.0.Alternatively or in combination, a reactive fluid may be added with theprecursor to the reaction zone which provides excess carbon or reducesexcess oxygen. Some illustrative examples include but are not limited tomethane, ethylene, acetylene, ethane, natural gas, benzene, naphtha, andhydrogen.

[0035] If the objective is to prepare a nitride, a preferred embodimentof this invention is to use a precursor with an oxygen-to-nitrogenelemental ratio in the precursor molecule less than 0.1 and morepreferably less than 1.0, and most preferably less than 2.0.Alternatively or in combination, a reactive fluid may be added with theprecursor to the reaction zone which provides excess nitrogen or reducesexcess oxygen. Some illustrative examples include but are not limited toamines, ammonia, hydrazine, nitrogen, and hydrogen.

[0036] When the objective is to prepare a boride, a preferred embodimentof this invention is to use a precursor with an oxygen-to-boronelemental ratio in the precursor molecule less than 0.1 and morepreferably less than 1.0, and most preferably less than 1.5.Alternatively or in combination, a reactive fluid may be added with theprecursor to the reaction zone which provides excess boron or reducesexcess oxygen. Some illustrative examples include, but are not limitedto, boranes, boron, and hydrogen.

[0037] When the objective is to prepare a carbonitride, a preferredembodiment of this invention is to use a precursor with (a)oxygen-to-carbon elemental ratio in the precursor molecule less than 0.1and more preferably less than 1.0, and most preferably less than 2.0,and (b) oxygen-to-nitrogen elemental ratio in the precursor moleculeless than 0.1 and more preferably less than 1.0, and most preferablyless than 2.0. Alternatively or in combination, a reactive fluid may beadded with the precursor to the reaction zone which provides excessnitrogen and carbon, or reduces excess oxygen. Some illustrativeexamples include, but are not limited to methane, ethylene, acetylene,ethane, natural gas, benzene, naphtha, amines, ammonia, hydrazine,nitrogen, and hydrogen.

[0038] While the above paragraphs specifically teach methods to preparehigh purity powders of oxides, carbides, nitrides, borides, andcarbonitrides, the teachings may be readily extended in analogous mannerto other compositions. While variations of the teachings herein thatallow impurities that may be easily removed from the powder bypost-processing may be permitted and practiced, it is recommended thatimpurities be avoided to begin with. While it is preferred to use hightemperature processing, a moderate temperature processing, or alow/cryogenic temperature processing may also be employed to producehigh purity fine powders.

[0039] Once the pure precursor is available, it is processed at hightemperatures to form the product powder. Products such as powdersproduced from these precursors are pure. It is important to ensure thatthe method of producing the product and the environment in which theseproducts are produced are pure and compatible with the chemistryinvolved. To illustrate but not limit, to ensure high purity in thefinal product, the material of construction for precursor pumping andpipes and the wall of the reactor should be inert to the precursor, thereaction intermediates, and the final products. Similarly, any oxidantsor diluents or secondary aids used to transform the precursor into theproduct should be of purity equal to or higher than that desired in thefinal product. In the preferred embodiment inerts such as argon, helium,and xenon are used wherever possible to shield the powders fromcontacting impurity generating environments. Furthermore, it ispreferred if oxidants, diluents, inerts, or secondary aids are used theyare purified to concentrations greater than 99.9%. To reduce costs,these gases may be recycled or mass/heat integrated or used to preparethe pure gas stream desired by the process.

[0040] The high temperature processing is conducted at step 103 attemperatures greater than 1000° C., preferably greater than 2000° C.,more preferably greater than 3000° C., and most preferably greater than4000° C. Such temperatures may be achieved by any method such as, butnot limited to, plasma processes, combustion, pyrolysis, and electricalarcing in an appropriate reactor. The plasma may provide reaction gasesor just provide a clean source of heat. The feed precursors may beinjected axially or radially or tangentially or at any angle to the hightemperature region. The precursor may be pre-mixed or diffusionallymixed with other reactants. The feed may be laminar, parabolic,turbulent, pulsating, sheared, cyclonic, or any other flow pattern. Onemay inject one or more precursors from one or more ports in the reactor.The feed spray system may yield a feed pattern that envelops the heatsource or alternatively, the heat sources may envelop the feed oralternatively, various combinations of this may be employed. A preferredembodiment is to atomize and spray the feed in a manner that enhancesheat transfer efficiency, mass transfer efficiency, momentum transferefficiency, and reaction efficiency. The reactor shape may becylindrical, spherical, conical, or any other shape. Method andequipment such as those taught in U.S. Pat. Nos. 5,788,738, 5,851,507,and 5,984,997 (and which are herewith incorporated by reference) areillustrations of various ways the teachings herein can be practiced.

[0041] In the preferred embodiment, the high temperature processingmethod has instrumentation that can assist quality control. Furthermoreit is preferred that the process is operated to produce fine powders104, preferably submicron powders, and most preferably nanopowders. Thegaseous products from the process may be monitored for composition,temperature and other variables to ensure quality (e.g., purity) at 105.The gaseous products may be recycled at step 107 or used as a valuableraw material when high purity powders 108 have been formed as determinedat step 106 in an integrated manufacturing operation.

[0042] Once the product fine powders 108 have been formed, it ispreferred that they be quenched to lower temperatures to preventagglomeration or grain growth such as, but not limited to, methodstaught in the U.S. Pat. No. 5,788,738. It is preferred that methods beemployed that can prevent deposition of the powders on the conveyingwalls. These methods may include electrostatic techniques, blanketingwith gases, higher flow rates, mechanical means, chemical means,electrochemical means, and/or sonication/vibration of the walls.

[0043] The product fine powders may be collected by any method. Someillustrative approaches without limiting the scope of this invention arebag filtration, electrostatic separation, membrane filtration, cyclones,impact filtration, centrifugation, hydrocyclones, thermophoresis,magnetic separation, and combinations thereof.

[0044]FIG. 2 shows a schematic flow diagram of a thermal process for thesynthesis of nanoscale powders as applied to precursors such as metalcontaining emulsions, fluid, or water soluble salt. Although a singleprecursor storage tank 204 is shown in FIG. 2, it should be understoodthat multiple precursor tanks may be provided and used with or withoutpremixing mechanisms (not shown) to premix multiple precursors beforefeeding into reactor 201. A feed stream of a precursor material isatomized in mixing apparatus 203. The precursor storage tank 204 mayalternatively be implemented by suspending the precursor in a gas,preferably in a continuous operation, using fluidized beds, spoutingbeds, hoppers, or combinations thereof, as best suited to the nature ofthe precursor. The resulting suspension is advantageously preheated in aheat exchanger (not shown) preferably with the exhaust heat and then isfed into a thermal reactor 201 where the atomized precursors arepartially or, preferably, completely transformed into vapor form. Thesource of thermal energy in the preferred embodiments is plasmagenerator 202 powered by power supply 206. Plasma gas 207, which may beinert or reactive, is supplied to plasma generator 202. Alternatively,the source of thermal energy may be internal energy, heat of reaction,conductive, convective, radiative, inductive, microwave,electromagnetic, direct or pulsed electric arc, nuclear, or combinationsthereof, so long as sufficient to cause the rapid vaporization of thepowder suspension being processed. Optionally, in order to preventcontamination of the vapor stream caused by partial sublimation orvaporization, the walls of reactor 201 may be pre-coated with the samematerial being processed.

[0045] The vapor next enters an extended reaction zone 211 of thethermal reactor 201 that provides additional residence time, as neededto complete the processing of the feed material and to provideadditional reaction and forming time for the vapor (if necessary). Asthe stream leaves the reactor 201, it passes through a zone 209 wherethe thermokinetic conditions favor the nucleation of solid powders fromthe vaporized precursor. These conditions are determined by calculatingthe supersaturation ratio and critical cluster size required to initiatenucleation. Rapid quenching leads to high supersaturation which givesrise to homogeneous nucleation. The zones 201, 209, and 211 may becombined and integrated in any manner to enhance material, energy,momentum, and/or reaction efficiency.

[0046] As soon as the vapor has begun nucleation, the process stream isquenched in heat removal apparatus within nucleation zone 209comprising, for example, a converging-diverging nozzle-driven adiabaticexpansion chamber (not shown) at rates at least exceeding 10.sup.3K/sec, preferably greater than 10.sup.6 K/sec, or as high as possible. Acooling medium (not shown) may be utilized for the converging-divergingnozzle to prevent contamination of the product and damage to theexpansion chamber. Rapid quenching ensures that the powder produced ishomogeneous, its size is uniform and the mean powder size remains insubmicron scale.

[0047] The quenched gas stream is filtered in appropriate separationequipment in harvesting region 213 to remove the high purity submicronpowder product 108 from the gas stream. As well understood in the art,the filtration can be accomplished by single stage or multistageimpingement filters, electrostatic filters, screen filters, fabricfilters, cyclones, scrubbers, magnetic filters, or combinations thereof.The filtered nanopowder product is then harvested from the filter eitherin batch mode or continuously using screw conveyors or gas-phase solidtransport. The product stream is then conveyed to powder processing orpackaging unit operations (not shown in the drawings).

[0048] In an alternative process shown in FIG. 3, the product finepowders instead of being harvested, may alternatively be depositeddirectly on a substrate to form a coating or film or near net shapestructural part. In this embodiment, the fluid precursor is thermallyheated to high temperatures to yield a hot vapor. A substrate with anexposed surface to be coated is provided within or in communication withreaction chamber 201 on, for example, a thermally controlled substrateholder 301. The hot vapor is then contacted with a substrate surfacethat needs to be coated. The hot vapor may be cooled or quenched beforethe deposition step to provide a stream that has fine liquid droplets orhot particulate matter. The substrate may be cooled or heated using asubstrate thermal control 302 to affect the quality of the coating.

[0049] The deposition approach in accordance with the present inventionis different from thermal spray technology currently in use in many wayssuch as but not limited to the following ways: (a) the feed is solidmicron sized powder in thermal spray processes, in contrast, in thisteaching the feed is a fluid precursor; (b) the thermal spray process isconsidered to yield a powder with molten surface which then sticks tothe substrate, in contrast, in this embodiment of the present invention,as the hot vapor cools it is anticipated to yield a molten droplet orsoft particulate that forms the coating. The advantage of formingcoating or film with the teachings herein is the fine to nanoscalemicrostructure of the resultant coating or film. Furthermore, it iscontemplated that the present invention will yield additional benefitsin the ability to easily transport fluids within the process, theability to form high purity coatings, and the ability to form wideranges of compositions (oxides, carbides, nitrides, borides, multimetalcompositions, composites, etc.) from a limited collection of precursorsthrough mixing and other methods as taught herein.

[0050] A coating, film, or component may also be prepared by dispersingthe high purity nanopowder and then applying various known methods suchas but not limited to electrophoretic deposition, magnetophorecticdeposition, spin coating, dip coating, spraying, brushing, screenprinting, ink-jet printing, toner printing, and sintering. Thenanopowders may be thermally treated or reacted to enhance electrical,optical, photonic, catalytic, thermal, magnetic, structural, electronic,emission, processing or forming properties before such a step.

Example 1 Magnesium Oxide

[0051] Magnesium acetate was dissolved in high purity water and pumpedas a liquid into a plasma reactor. To ensure complete oxidation, pureoxygen was fed into the process. The core temperature of the plasma wasgreater than 6000° C., while the outer edge temperature was estimated tobe greater than 3000° C. The plasma was produced using a DC arc andargon as the plasma gas. The precursor completely vaporized when itinteracted with the plasma. The metal vapor oxidized completely. Thevapor was slightly cooled to encourage the formation of nanopowder. Thenanopowder containing stream was quenched in a converging divergingnozzle (to >10³ ° C./sec) in flowing oxygen. The powder was harvestedusing membrane bags and a venturi cyclone fed with compressed air forsuction effect. The collected powder was high purity magnesium oxide(MgO) with surface area greater than 100 m²/gm and mean size less than10 nm. Over a two hour run, over 100 grams of powder were harvested.This example illustrated that fine powders, more specificallynanopowders of simple oxides can be manufactured.

Example 2 Magnesium Oxide

[0052] In another run, magnesium acetate (Reagent Grade 1271R, ShepherdChemical Company, Cincinnati, Ohio, USA) was dissolved in high puritywater and pumped as a liquid into a plasma reactor. The feed had thefollowing impurities on metal basis (K: 35 ppm, Na: 203 ppm, Fe: 88 ppm,Ca: 27 ppm, Ba: <9 ppm, Mn: 53 ppm, Sr: <9 ppm). To ensure completeoxidation, pure oxygen was fed into the process at a faster rate than inExample 1. The core temperature of the plasma was greater than 6000° C.,while the outer edge temperature was estimated to be greater than 3000°C. The plasma was produced using a DC arc and argon as the plasma gas.The precursor completely vaporized when it interacted with the plasma.The vapor oxidized completely. The vapor was slightly cooled toencourage the formation of nanopowder. The nanopowder containing streamwas quenched in a converging diverging nozzle (to >10³ ° C./sec) inflowing oxygen. The powder was harvested using membrane bags and aventuri cyclone fed with compressed air for suction effect. Thecollected powder was high purity magnesium oxide (MgO) with surface areagreater than 50 m²/gm and mean size less than 20 nm.

[0053] The purity of the fine powder was determined using direct currentplasma. The impurities in the fine powder produced were as follows onmetal basis (K: 38 ppm, Na: 189 ppm, Fe: 89 ppm, Ca: <10 ppm, Ba: <10ppm, Mn: 41 ppm, Sr: <10 ppm). In other words, the fine powder producedwas over 99.9% pure on metal basis. Given that the product powder wasstatistically as pure as the feed precursor, this example illustratedthat fine powders, and more specifically nanopowders, of high purityoxides can be manufactured from high purity fluids. Such high purityoxides are needed in structural, electronic, photonic, telecom,catalytic, thermal, electrochemical, biomedical, chemical, sensor,optic, electromagnetic, instrumentation, sputtering and energy products.

Example 3 Indium Tin Oxide

[0054] Indium octoate and tin octoate were mixed in a specified ratio bymetal basis. Indium-tin-oxide (ITO) powders with grain size less than 20nm were produced using the process of Example 1. This exampleillustrated that fine powders, and more specifically nanopowders, ofhigh purity complex multimetal oxides can be manufactured from fluids.Such high purity multimetal oxides are desired in numerous applicationssuch as, but not limited to, coatings for EMI shielding, electronic,electromagnetic, device, thermal, catalytic, photonic, optical,electrochemical, chemical, sensor, other films/coatings,instrumentation, sputtering and biomedical applications.

Example 4 Nickel

[0055] Nickel octoate in mineral spirits was pumped as a liquid into theplasma reactor with pure oxygen as in Example 1. Nitrogen gas was addedat the entrance and exit to the nozzle as the quenching gas. Thecollected powder was primarily metallic nickel based on X-raydiffraction analysis and had a surface area of 9 to 24 m²/g and meansize of 30 to 75 nm. The largest particles observed were less than 1micron. This example presented an unusual result, i.e., that plasmaprocessing can yield a metal powder even when oxygen is present with anorganic precursor. Normally, combustion of metal containing organicswith oxygen yields metal oxides. This example illustrated that metalpowders can be synthesized from metal containing organics in thepresence of oxygen when processed at high enough temperatures, i.e.greater than 2000° C., preferably greater than 3000° C., and mostpreferably greater than 4000° C. This example also illustrated that finepowders, and more specifically nanopowders, of metals can bemanufactured. Fine sub-micron and nanoscale nickel powders are neededfor battery, capacitor and other passive electronic componentelectrodes, electromagnetic shielding and other applications. Additionalapplications of high purity metal fine powders include, but are notlimited to, structural, electronic, electromagnetic, device, thermal,catalytic, photonic, optical, electrochemical, chemical, films/coatings,sensor, instrumentation, sputtering and biomedical applications.

[0056] The composition of the powder produced can be varied bycontrolling the secondary feed gas added. For example, smallconcentrations of oxygen can yield a non-stoichiometric oxide.Additionally, if methane or ammonia are added, the product powder is ofnon-stoichiometric or stoichiometric oxycarbide, oxynitride, carbide,nitride, and carbonitride composition.

Example 5 Carbon-doped Silicon Carbide

[0057] Octa-methyl-cyclo-tetra-siloxane was pumped into the plasmareactor with argon as in Example 1. Nitrogen gas was added at theentrance and exit to the nozzle as the quenching gas. The collectedsilicon carbide powder contained less than 6% free carbon and less than9% oxygen and had a surface area >100 m²/g. Over a one hour run time 950grams of powder were harvested. The percentage of carbon and oxygen werevaried by controlling the feed composition, feed rate, feed material,and other reactor variables. This example illustrated that fine powders,and more specifically nanoscale powders, of carbon doped carbides andinterstitial alloys can be manufactured. Such powders are needed inabrasives and structural products markets. Additional applications ofhigh purity carbide powders include, but are not limited to, structural,electronic, electromagnetic, device, thermal, catalytic, photonic,optical, electrochemical, chemical, films/coatings, sensor,instrumentation, sputtering and biomedical applications.

Example 6 Iron/Iron Oxide

[0058] Iron salt of mixed napthenic acids and carboxylic acid was pumpedinto the plasma reactor with argon as in Example 1. Nitrogen and argongases were added at the entrance and at the exit to the nozzle as thequenching gas. Based on x-ray diffraction analysis, the major phase ofthe collected powder was iron with a minor amount of iron oxide (FeO).The powder had a surface area of 19 m²/g and mean size of 40 nm. Byusing oxygen in place of argon and nitrogen, Fe₂O₃ and Fe₃O₄ wasproduced by using different nozzle with narrow opening (rapid quench),Fe₃O₄ was produced with surface area of 26 m²/gm and a mean size of 43nm. Using a nozzle with a larger opening (slower quench), Fe₂O₃ wasproduced with surface area of 16 m²/gm and a mean size of 72 nm.

[0059] This example again illustrated that metallic powders from organicprecursors may be produced using high temperature process. Furthermore,the example illustrated that fine powders, and more specificallynanoscale powders, of nanocomposites and magnetic materials (Fe/Feo) canbe manufactured. The example also illustrates the flexibility ofproducing different compositions by utilizing changes in the gasenvironment and the reactor component design. Applications of highpurity composite powders are, but are not limited to, structural,electronic, electromagnetic, device, thermal, catalytic, photonic,optical, electrochemical, chemical, films/coatings, sensor,instrumentation, sputtering and biomedical applications.

Example 7 Yttrium Oxide

[0060] Yttrium octoate was pumped into the plasma reactor with oxygen asin Example 1. Oxygen was used as the quenching gas. The yttrium oxidepowder produced had a surface area greater than 39 m^(2/)g and mean sizeof less than 30 nm. Fine powder such as yttria can be used at lowconcentrations in ceramic compositions used in the multilayer ceramiccapacitor industry where it is desirable to uniformly disperse thisadditive (or dopant) material through out the bulk ceramic composition.

Example 8 Multimetal Oxides

[0061] Multimetal precursors as identified in Table 1 were mixed andthen pumped into the plasma reactor with oxygen as in Example 1. As anon-limiting example, BaZrO₃ was produced by mixing the precursor forbarium and zirconium in appropriate stoichiometric ratio which then wasfed into the reactor. Oxygen was used as the quenching gas. Table 2presents the compositions produced and their observed characteristics.Fine powder such as multimetal oxides (titanates, zirconates, silicates,manganates, ferrites, doped ceria) can be used as dopants and additivesin the single layer and multilayer electroceramic and magnetoceramiccomponents industry where it is desirable to uniformly disperse thisadditive (or dopant) material through out the bulk ceramic composition.Multimetal compositions are also useful in batteries, fuel cells,catalysts, biomedical implants, sintering aids, sputtering targets,thermal, and optical applications. TABLE 1 Desired Composition PrecursorBarium Barium Carboxylate (OMG PLASTISTAB 2116) Zirconium Zirconium2-ethylhexanoate (SHEPHARD Zr VERSALATE 1394) Aluminum Aluminum organiccomplex (OMG 7% AOC) Calcium Calcium dimethylhexanoate (SHEPHARD CaVersalate 1424) Silicon Octamethylcyclotetrasiloxane (GELEST S106700.0)Cerium Cerium 2-ethylhexanoate (OMG 12% Cerium Hex-Cem 1024) TitaniumTetrakis (2-ethylhexyl) titanate (DUPONT TYZOR TOT)

[0062] TABLE 2 Particle Size (nm, XRD Surface Area Particle SizeScherrer Composition (m²/gm) (nm) Analysis) BaZrO₃ >30 <30 BaTiO₃ >20<50 CaZrO₃ >15 <75 <65 CaTiO₃ >20 <70 CeO₂ >50 <20 <20 Al₂O₃.SiO₂ >15<150 <75

USES

[0063] High purity fine powders have numerous applications in industriessuch as, but not limited to, biomedical, pharmaceuticals, sensor,electronic, telecom, optics, electrical, photonic, thermal, piezo,magnetic, catalytic and electrochemical products. For example,biomedical implants and surgical tools can benefit from higher puritypowders. Powdered drug carriers and inhalation particulates that reduceside effects benefit from purer powders. Sputtering targets forelectronic quality films and device fabrication offer improvedperformance and reliability with higher purities. Such sputteringtargets can be prepared from fine powders using isostatic pressing, hotpressing, sintering, tape casting, or any other technique that yieldshigh density compact. Optical films prepared from higher purity powdersoffer more consistent refractive index and optical performance. Passivecomponents such as capacitors, inductors, resistors, thermistors, andvaristors offer higher reliability if powder purity is more reliable.Electrochemical capacitors prepared from higher purity powders offerhigher charge densities, high volumetric efficiencies, and longer meantimes between failures. Batteries prepared from higher purity powdersoffer longer shelf life, longer operational times, more capacity, andsignificantly superior performance. Chemical sensors prepared fromhigher purity powder be more selective and sensitive. Catalyticmaterials that are prepared from purer powders last longer and givesuperior selectivity. Magnetic devices prepared from purer powders areexpected to offer superior magnetic performance. Purer powder basedcomposites are expected to be more corrosion resistant. In general,purer powders offer a means of improving the value-added performance ofexisting products that are produced from less pure powders.

[0064] Other embodiments of the invention will be apparent to thoseskilled in the art from a consideration of the specification or practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with the true scope andspirit of the invention being indicated by the following claims.

1. A process for producing fine metal powder comprising: providing afeed composition wherein the feed composition comprises a fluidprecursor; processing the precursor at a temperature greater than 2000°C. in a gas comprising oxygen; and transforming the precursor to finemetal powder.
 2. The process of claim 1, where the temperature isgreater than 3000° C.
 3. The process of claim 1, wherein the fine metalpowder comprises a submicron powder.
 4. The process of claim 1, whereinthe fine metal powder comprises a nanoscale powder.
 5. The process ofclaim 1, wherein the purity of the fine metal powder is greater than99.9% on metal basis.
 6. The process of claim 1, wherein the purity ofthe fine metal powder is greater than 99.99% on metal basis.
 7. Theprocess of claim 1, wherein the fine metal powder comprises a multimetalcomposition.
 8. The process of claim 1, wherein the fine metal powdercomprises nickel.
 9. The process of claim 1, wherein the fine metalpowder comprises a metal from the group consisting of: aluminum,silicon, titanium, and zirconium.
 10. The process of claim 1, whereinthe fine metal powder comprises a metal from the group consisting of:iron and copper.
 11. A process for producing fine metal powdercomprising: providing a feed precursor; processing the feed precursor ata temperature greater than 2000° C. in a plasma reactor in a gascomprising oxygen; and transforming the feed precursor to fine metalpowder.
 12. The process of claim 11, where the temperature is greaterthan 3000° C.
 13. The process of claim 11, wherein the fine metal powdercomprises a submicron powder.
 14. The process of claim 11, wherein thefine metal powder comprises a nanoscale powder.
 15. The process of claim11, wherein the purity of the fine metal powder is greater than 99.9% onmetal basis.
 16. The process of claim 11, wherein the purity of the finemetal powder is greater than 99.99% on metal basis.